1. Field of the Invention
Embodiments of the present invention generally relate to methods and apparatus for improving top drive operations.
2. Description of the Related Art
It is known in the industry to use top drive systems to rotate a drill string to form a borehole. Top drive systems are equipped with a motor to provide torque for rotating the drilling string. The quill of the top drive is typically threadedly connected to an upper end of the drill pipe in order to transmit torque to the drill pipe. Top drives may also be used in a drilling with casing operation to rotate the casing.
To drill with casing, most existing top drives use a threaded crossover adapter to connect to the casing. This is because the quill of the top drives is typically not sized to connect with the threads of the casing. The crossover adapter is design to alleviate this problem. Generally, one end of the crossover adapter is designed to connect with the quill, while the other end is designed to connect with the casing. In this respect, the top drive may be adapted to retain a casing using a threaded connection.
However, the process of connecting and disconnecting a casing using a threaded connection is time consuming. For example, each time a new casing is added, the casing string must be disconnected from the crossover adapter. Thereafter, the crossover must be threaded to the new casing before the casing string may be run. Furthermore, the threading process also increases the likelihood of damage to the threads, thereby increasing the potential for downtime.
As an alternative to the threaded connection, top drives may be equipped with tubular gripping heads to facilitate the exchange of wellbore tubulars such as casing or drill pipe. Generally, tubular gripping heads have an adapter for connection to the quill of top drive and gripping members for gripping the wellbore tubular. Tubular gripping heads include an external gripping device such as a torque head or an internal gripping device such as a spear. An exemplary torque head is described in U.S. Patent Application Publication No. 2005/0257933, filed by Pietras on May 20, 2004, which is herein incorporated by reference in its entirety. An exemplary spear is described in U.S. Patent Application Publication Number US 2005/0269105, filed by Pietras on May 13, 2005, which is herein incorporated by reference in its entirety.
In most cases, the adapter of the tubular gripping head connects to the quill of the top drive using a threaded connection. The adapter may be connected to the quill either directly or indirectly, e.g., through another component such as a sacrificial saver sub. One problem that may occur with the threaded connection is inadvertent breakout of that connection during operation. For example, in a drilling with casing operation, a casing connection may be required to be backed out (i.e., unthreaded) either during the pulling of a casing string or to correct an unacceptable makeup. It may be possible that the left hand torque required to break out the casing connection exceeds the breakout torque of the connection between the adapter and the quill, thereby inadvertently disconnecting the adapter from the quill and creating a hazardous situation on the rig.
There is a need, therefore, for methods and apparatus for ensuring safe operation of a top drive.